The human foot is an extremely complicated bio-mechanism having 28 bones. These bones are generally grouped in the tarsus (ankle) which includes the talus and calcaneus (heel); the metatarsus which forms (the traverse and longitudinal "arches" of the foot); and the phalanges (toes); and the bones themselves are interconnected through joints operative through 19 muscles, 117 ligaments, and associated nerves, blood vessels, and tissue. The interrelationship of the bones of the foot and the complex biomechanics of the foot during standing, walking and running movements have long been studied and analyzed by the medical profession. In this regard, it is well-known that during walking and running, each foot in action progresses through a series of motions from the moment the heel alone impacts or strikes the ground through a "transitional" or "midstance" phase in which the plantar portions of the foot are generally horizontal and in substantially full contact with the ground through the final propulsive or pushing off phase in which the toes leave the ground as they propel the body forward. Together, the aforementioned three periods of foot contact comprise that phase of the " gait" which is known as the "stance" phase. When the foot is off the ground and moving forward, it is in the other portion of the gait cycle known as the "swing" phase. (See FIG. 6).
It is also well-known that the foot is involved in complex movement about the three body planes when the foot is in the transitional phase of the stance during walking or running.
Specifically the body planes are the horizontal or transverse plane which divides the body into upper and lower portions; the sagittal plane, which divides the body, vertically front-to-back, into right hand and left hand sections; and the frontal plane which divides the body, vertically side-to-side, into anterior and posterior portions. Similarly, three body planes, which are mutually perpendicular, divide each foot as follows:
1. The horizontal plane divides the foot into dorsal (top) and plantar (bottom) portions. PA1 2. The sagittal plane divides the foot into medial (inner) and lateral (outer) portions. PA1 3. The frontal plane divides the foot into distal (furthest from the leg) and proximal (closest to leg) portions.
In connection with each of the body planes there is pure motion of the foot (motion that takes place on one plane with the action of the motion on the other two planes). With regard to the horizontal plane, the foot is subject to abduction and adduction, which are movements of the distal portion of the foot away or toward the midline of the body. With regard to the sagittal plane, the foot is subject to dorsiflexion and plantarflexion involving movement of a part of the entire foot toward or away from the anterior aspect of the leg. With regard to the frontal plane, the foot is subject to inversion and eversion, which motions involve movement of a part of the foot or the whole foot, in which the plantar surface is canted toward or away from the body midline.
In addition to the aforementioned "pure motions" of the foot, namely abduction and adduction; dorsiflexion and plantarflexion; inversion and eversion; the foot is subject to complex motions in which the axis of the motion forms an angle with the three body planes and the motion takes place simultaneously in all of the body planes. This type of motion involves a combination of the aforementioned pure motions and is called "pronation" and "supination".
More specifically, pronation of the foot is a motion which has components in all three body planes, and motion in one of these planes cannot take place independently of the other two. The motion of pronation is a complex motion comprising dorsiflexion, abduction and eversion of the distal on the proximal part. The axis of the motion is an eccentric one which is inclined at an angle to all three body planes, and passes from posterior, plantar and lateral, to anterior, dorsal and medial. In a closed kinetic chain, i.e. during stance, the calcaneus everts with pronation, while the talus adducts and plantarflexes. Additionally, pronation occurs at the midtarsal joint simultaneously due to the forces present on the forefoot. Supination of the foot takes place about the same axis as pronation and consists of a complex motion in a direction opposite to that of pronation, namely; plantarflexion, adduction and inversion of the distal on the proximal parts. In a closed kinetic chain, i.e. during stance, the calcaneus inverts with supination, while the talus abducts and dorsiflexes.
The medical profession and podiatrists have long recognized that comfort, maximum efficiency and preservation of function of the foot are dependent upon the normal progression, distribution and dissipation of the effects of the dynamic forces acting on the skeletal structure of the foot and leg during running and walking. The well-constructed and properly balanced shoe should be in balance with the skeletal-bearing points of the foot and should accommodate and synchronize with its actions. Unfortunately, these criteria in providing comfortable balanced and synchronized shoe constructions have not been widely employed by the shoe industry in the large scale manufacture of footwear by mass production techniques; rather they appear to have been limited mostly to custom made orthopedic shoes. Accordingly, it is to a simplified, efficient, balanced and synchronized running shoe construction, which may be readily mass-produced to which the present invention is directed.